Early events in the interaction between maize and Southern rust

Puccinia polysora, the incitant of Southern rust in maize was used to infect maize inbreds B37 and B37R which are nearly isogenic except for a single dominant gene for resistance in B37R. A method was devised that permits high numbers of infections in a localized region of leaf tissue. After overnight treatment in a dew chamber to initiate fungal growth, comparisons between treated and control plants of each cultivar showed that: 1. There was considerably less penetration of the resistant cultivar by P. polysora, but the pathogen was able to penetrate and colonize the leaf tissue in both cultivars. Over the 48 hour period that histological sections were made, there was a progressive lag in the growth of the fungus at all stages of the infection process in B37R. 2. Synthesis of a specific protein was induced within 16 hours of inoculation in both B37 and B37R as detected by pulse labeling with35S-methionine. 3. No change in activity that could he associated with an induced defense response was detectable for any of several phenylpropanoid pathway enzymes (shikimate dehydrogenase, cinnamyl-alcohol dehydrogenase, polyphenol oxidase, and peroxidase) that were examined using isoelectric focusing or native polyacrylamide gel electrophoresis to separate isozymes. 4. Peroxidase activity in specific isozymes developed more rapidly in B37R than in B37 over the 48h post-inoculation period examined, but the differences were seen in both control and infected samples.

Early events in the interaction between maize and Southern rust Academic Article